Dynamic Respiration Index Research Articles

Biological compost stability influences odor molecules production measured by electronic nose during food-waste high-rate composting

Composting is a technique that is used to convert organic waste into agriculturally useful products. Composting is an aerobic, solid-state biological process, which typically can be divided into two phases, a high-rate composting phase and a curing phase. High-rate composting plays an important role during the composting process, owing to the high microbial activity occurring during this phase. It requires an accurate plant design to prevent the formation of anaerobic conditions and odors. The formation of anaerobic conditions mainly depends on the rate of O 2 consumption needed to degrade the substrate, i.e., the biological stability of the substrate. In this study, we investigated the relationship between the biological activity, measured by the dynamic respiration index (DRI) and the odor molecules production, measured by an electronic nose (EN) during two food-waste high-rate composting processes. Although the O 2 concentration in the biomass free air space (FAS) was kept optimal (O 2 > 140 ml l − 1 , v/v) during composting, strong anaerobic conditions developed. This was indicated by the high levels of sulfur compounds, methane, and hydrogen in the outlet air stream. Both the high level of O 2 consumption, needed to degrade the high-degradable water-soluble organic matter and the low water O 2 solubility, caused by high temperature reached in this stage (up to 60 °C), led to the anaerobic conditions observed in the biofilm-particle level. The application of the partial least square (PLS) analysis demonstrated a good regression between the DRI and the odor molecules produced that was detected by the EN ( R 2 = 0.991; R 2 CV = 0.990), signifying the usefulness of the DRI as a parameter to estimate the potential production of odor molecules of the biomass.

Decline in microbial activity does not necessarily indicate an end to biodegradation in MSW-biowaste: A case study

The aim of this study was to examine whether a decline in microbial activity (i.e., CO 2 output) during the biodegradation of municipal solid waste (MSW) indicated an end to biodegradation and the appearance of a stable, final product. As the organic fraction of MSW was biodegraded in an 8 clamp Cambridge Batch System composter, CO 2 output declined by 50% and moisture content at the end of the process was <20%. Levels of biodegradable material remaining in the product were determined by the dynamic respiration index (DRI) method but despite 151 days in the composting system biodegradable material was still present at levels (24130 mg O 2/kg dry matter (DM)) which exceeded draft EU biowaste directive (2001) guidelines (10,000 mg O 2/kg DM). Further laboratory based incubations demonstrated that microbial activity and hence biodegradation of organic material could be restarted if moisture levels were adjusted suggesting that dehydration limited microbial activity. Low levels of microbial activity alone did not therefore indicate and end to biodegradation, biodegradable material was not exhausted and the final product was not stable which has serious implications for its end-use.

An index for quantifying the aerobic reactivity of municipal solid wastes and derived waste products

The organic matter contained in municipal solid waste (MSW) and in the MSW fractions obtained by mechanical separation has strong environmental impact when the waste is used as landfill. This is partly due to the biological activity that occurs under anaerobic conditions. Negative effects on the environment include unpleasant odors, biogas, leachate and biomass self-heating. Measuring the biological reactivity of waste with the help of indicators is an important tool to prevent waste impact. The aim of this study was to develop an index capable of describing the aerobic reactivity of waste, using both biological and chemical indicators. To develop this index, 71 MSW and MSW-product samples, including biologically treated MSW and mechanically separated MSW fractions, were analyzed. Fifty of the 71 samples analyzed represented MSWs and their derived products collected from a number of Italian waste plants and sites. The remaining 21 were MSW samples collected at different times during 8 different full-scale aerobic biological processes in four treatment plants used to reduce the biological reactivity of wastes. Five of these processes used the entire (unsorted) MSW, while the remaining three used the organic fraction of the MSW obtained by mechanical pre-treatment (waste sieving). Respirometric activity (Dynamic Respiration Index, DRI) and eluates characterization (chemical oxygen demand — COD, and 5 days biological oxygen demand — BOD5) were used as indicators of waste strength, as they had previously been reported to be indirect measures of waste impact on landfill. Summarizing all studied indicators, Principal Component Analysis (PCA) was used to develop the Putrescibility Index (Ip). The results revealed Ip index of 204±33 (mean±standard deviation) and 159±14 for the organic fraction of MSW and MSW untreated waste respectively, and of 106±16 and 101±22 for the corresponding biologically treated waste.

Influence of different co-substrates biochemical composition on raw sludge co-composting

The influence of biochemical composition of different co-substrates added to raw sludge during co-composting process was studied. The physical properties of the composting mass and their influence on the biological activity were also investigated. Three treatments composed of mixtures of raw sludge and co-substrate (commercial fats, protein, and cellulose) were carried out and compared to a control composed of raw sludge. Mixture conditioning was performed on the basis on air filled porosity (40%). The results obtained in the co-composting processes reflected a higher biological activity and higher degradation percentages of dry and organic matter when compared with control. Higher temperatures (60, 67 and 62 degrees C for fats, protein and cellulose, respectively) were also achieved in all co-composting experiments as compared to the control test (55 degrees C). Biological activity was measured using both Static and Dynamic Respiration Indices obtaining higher values in co-composting experiments compared to the control test. Fats content reduction was higher (66%) at higher fats content in the initial mixture (10.6%). The addition of fats seems also to promote the degradation of cellulose and lignin. Co-composting experiments with fats and cellulose presented higher initial C/N ratio and lower nitrogen losses, 27.5 and 34.2% compared to 40% for raw sludge. It has been demonstrated that the addition of an adequate co-substrate to raw sludge leads to a higher degradation percentages of the different biochemical fractions and higher nitrogen conservation.

Determination of biological stability in compost: A comparison of methodologies

Biological [dynamic respiration index (DRI); chemical humification indexes: humification index (HI), degree of humification (DH) and humification rate (HR); and thermoanalytical (thermostability index, R 1 and a labile fraction)] indexes were used to assess compost stability of 15 end products. By use of these three techniques independent assessment of compost stability was made possible. Evidence of unstable materials was found where labile, easily biodegradable, and non-humified organic fractions were present. The DRI was used as a reference index for biological stability, and no significant correlation was observed between DRI and the humification indices (HI, DH, HR) and the thermogravimetry index ( R 1). On the other hand, significant correlation was observed for DRI vs. non-humified carbon (NHC), which was determined using the chemical method and the labile fraction determined by thermogravimetry, as well as for NHC vs. “labile fraction”. These fractions represent labile, easily biodegradable, and non-humified organic matter. Significant correlations were also observed between the three above mentioned measurements and TEC, suggesting that this fraction is mainly formed of the easily degradable organic fraction. These results suggest that the integrated use of biological, chemical, and thermoanalytical methods could represent a useful tool in differentiating stabilized composts from non-stabilized ones, and it could provide more reliable information for both managerial and sanitary health aspects involved in good agricultural practice.

The determination of biological stability of composts using the Dynamic Respiration Index: The results of experience after two years

Biological stability was ascertained by using the Dynamic Respiration Index (DRI) on 144 samples of compost during the years 2003 and 2004, as a routine service for private subjects. Data obtained were collected and are critically discussed in this paper by using other parameters registered during tests, i.e., biomass temperature ( T), specific airflow rate ( Q s) and biomass analytical data (pH). Good linear correlations were obtained for DRI vs. T, DRI vs. Q s and DRI vs. pH, confirming expected results based on the theoretical discussion. Consequently, using the analytical method proposed in this paper means both T and Q can be used as additional parameters for measurement of the biological stability of compost. As a result, T values of 25.8 and 30.5 °C, and specific airflow rate of 8.6 and 13.4 m 3 Mg −1 VS h −1 were found corresponding to 500 and 1000 mg O 2 kgVS −1 h −1, which, respectively, indicate a high and a medium degree of biological stability.

Dynamic respiration index as a descriptor of the biological stability of organic wastes.

Analytical methods applicable to different organic wastes are needed to establish the extent to which readily biodegradable organic matter has decomposed (i.e., biological stability). The objective of this study was to test a new respirometric method for biological stability determination of organic wastes. Dynamic respiration index (DRI) measurements were performed on 16 organic wastes of different origin, composition, and biological stability degree to validate the test method and result expression, and to propose biological stability limits. In addition, theoretical DRI trends were obtained by using a mathematical model. Each test lasted 96 h in a 148-L-capacity respirometer apparatus, and DRI was monitored every hour. The biological stability was expressed as both single and cumulative DRI values. Results obtained indicated that DRI described biological stability in relation to waste typology and age well, revealing lower-stability waste characterized by a well-pronounced DRI profile (a marked peak was evident) that became practically flat for samples with higher biological stability. Fitting indices showed good model prediction compared with the experimental data, indicating that the method was able to reproduce the aerobic process, providing a reliable indication of the biological stability. The DRI can therefore be proposed as a useful method to measure the biological stability of organic wastes, and DRI values, calculated as a mean of 24 h of the highest microbial activity, of 1000 and 500 mg O(2) kg(-1) volatile solids (VS) h(-1) are proposed to indicate medium (e.g., fresh compost) and high (e.g., mature compost) biological stabilities, respectively.

Biostabilization of municipal solid waste

A mechanical–biological process for municipal solid waste (MSW) treatment was monitored for one year. Mechanical pre-treatment provided two fractions. The oversize fraction (∅>50 mm) (yield of 600 g kg −1 ww) (46 Mg day −1) was used for refuse derived fuel production, after undergoing a mechanical refining processes, because of low moisture content (200–250 g kg −1) and high calorific value (2500–2800 kcal kg ww −1). The undersize fraction (∅<50 mm) (yield 400 g kg −1 ww) (30 Mg day −1) contained about 800 g kg −1 of the MSW organic matter. This fraction was biologically treated using an aerobic process with an organic waste fraction from separate collection (77 Mg day −1) and recycled stabilized material (62 Mg day −1) obtained from end-product sieve (∅<20 mm) used as bulking agent. A retention time of three weeks was sufficient to obtain stabilized products in agreement with up-dated rules of the Lombardy Region (North Italy) regarding biostabilization and composting processes. Dynamic Respiration Index (DRI), such as required by both Lombardy Region rules and suggested by the European Community, was chosen in preference to other indices in order to assess the degree of biological stability of the end products. A mean DRI value of 1164 mg O 2 kg SV −1 h −1 was obtained and is in agreement with the proposed limit of 1000 ± 200 mg O 2 kg SV −1 h −1. Self-heating test, potential biogas production and fermentable volatile solids were also used as parameters to describe the potential impact of treated waste, providing further useful information. Nevertheless, all of these methods revealed analytical or interpretative limits. A complete mass balance of the biological treatment section showed that, from a net input of 107 Mg day −1, only 250 g kg −1 (27 Mg day −1) of the waste needed to be landfilled, with 750 g kg −1 (80 Mg day −1) being lost as CO 2 and H 2O.

The influence of biomass temperature on biostabilization–biodrying of municipal solid waste

A laboratory study was carried out to obtain data on the influence of biomass temperature on biostabilization–biodrying of municipal solid waste (initial moisture content of 410 g kg wet weight (w.w.) −1). Three trials were carried out at three different biomass temperatures, obtained by airflow rate control ( A=70 °C, B=60 °C and C=45 °C). Biodegradation and biodrying were inversely correlated: fast biodrying produced low biological stability and vice versa. The product obtained from process A was characterized by the highest degradation coefficient (166 g kg TS 0 −1; TS 0 −1 = initial total solid content) and lowest water loss (409 g kg W 0 −1; W 0 = initial water content). Due to the high reduction of easily degradable volatile solid content and preservation of water, process A produced the highest biological stability (dynamic respiration index, DRI=141 mg O 2 kg VS −1; VS = volatile solids) but the lowest energy content (EC = 10,351 kJ kg w.w. −1). Conversely, process C which showed the highest water elimination (667 g kg W 0 −1), and lowest degradation rate (18 g kg TS 0 −1 ) was optimal for refuse-derived fuel (RDF) production having the highest energy content (EC = 14,056 kJ kg w.w. −1). Nevertheless, the low biological stability reached, due to preservation of degradable volatile solids, at the end of the process (DRI = 1055 mg O 2 kg VS −1 ), indicated that the RDF should be used immediately, without storage. Trial B showed substantial agreement between low moisture content (losses of 665 g kg W 0 −1), high energy content (EC = 13,558 kJ kg w.w. −1) and good biological stability (DRI = 166 mg O 2 kg VS −1 ), so that, in this case, the product could be used immediately for RDF or stored with minimum pollutant impact (odors, leaches and biogas production).

00/02009 The U.S. wind market is back

The Landfill Directive (1999/31/EC) forces European States to reduce the amount of biodegradable municipal waste landfilled to 35% of 1995 levels. Mechanical-Biological Treatment (MBT) plants are the main alternative to waste incineration and landfilling. In this work, the waste treatment efficiency of six full-scale MBT facilities has been analysed using respiration indices (Dynamic Respiration Index and Cumulative Oxygen Consumption) to monitor plant performance. MBTs relying on anaerobic digestion plus composting achieved a high grade of stability on final compost (0.24 ± 0.09 mg O2 g−1 DM h−1 and 20 ± 9 mg O2 g−1 DM for dynamic respiration and cumulative consumption, respectively). On the contrary, MBTs relying only on composting showed a poor performance (1.3 ± 0.2 mg O2 g−1 DM h−1 and 104 ± 18 mg O2 g−1 DM for dynamic respiration and cumulative consumption, respectively). These results highlight the usefulness of respirometric balances to assess the performance of MBT full-scale plants.